HR: 14:10h
AN: B23G-03    [Abstracts]
TI: Iron Cycling at Loihi Seamount
AU: * Emerson, D
EM: demerson@bigelow.org
AF: Bigelow Laboratory for Ocean Sciences, PO Box 475, West Boothbay Harbor, ME 04575- 0475, United States
AB: Loi"hi is an active submarine volcano located close to the island of Hawai"i at a depth around 1100 m. The summit is host to a variety of focused and diffuse flow hydrothermal vent sites, which have in common a chemistry that is dominated by the presence of Fe(II) often in concentrations of 10's to 100's of μM at circumneutral pH. An outcome of these conditions is the deposition of substantial quantities of rust-colored microbial mats that are dominated by Fe-oxidizing bacteria (FeOB). These mat communities were first sampled in the late 1980s, and have subsequently been the subject of continued investigation, to the extent that Loih'i is now a model system for understanding deep-sea microbial communites that are primarily driven by iron-based lithotrophic metabolism. While the role of FeOB is becoming well-established, the short-term fate of the iron oxyhydroxides that are produced is less well understood, and specifically that role that Fe-reducing bacteria may have in re-cycling Fe(III) to Fe(II). A recent cruise to Loihi in 2006 found that one vent site, which has been slowly decreasing in activity, was essentially "dead", i.e. there was no sign of fluid flow or temperature anomaly. Yet, iron mats several cm thick persisted and chemical analysis suggested O2 penetrated the mat and that no Fe(II) was present, i.e. there no sign of active Fe-reduction. This raises the question of how active is the iron cycle in Loih'i iron mats? Experiments to measure Fe- reduction potential in Lohi"i mats do show activity and it is possible to enrich Fe-reducing bacteria. We have recently isolated a novel Geothermobacter sp. HR-1 from a Loih'i mat, that is an Fe-reducer and grows at mesophilic temperatures. This work will report on continued investigations into the iron cycle at Loih'i to further constrain the chemical conditions, further elucidate the potential for Fe-reduction in natural mat samples, and present the outcome of growing native isolates of Fe- oxidizers and reducers from Loih'i in co-culture.
DE: 0414 Biogeochemical cycles, processes, and modeling (0412, 0793, 1615, 4805, 4912)
DE: 0448 Geomicrobiology
DE: 0463 Microbe/mineral interactions
DE: 0471 Oxidation/reduction reactions (4851)
SC: Biogeosciences [B]
MN: 2007 Fall Meeting